Discoloration of construction surfaces due to algae growth or other agents has been a problem for the construction industry for many years. Discoloration has been attributed to the presence of blue-green algae and other airborne contaminants, such as soot and grease.
One approach to combating this problem is to coat the construction surfaces with a composition that contains photocatalysts and a binder, typically a silicate binder. When exposed to sunlight, the photocatalysts may photo-oxidize the organic materials that cause the discoloration.
Photocatalytic titanium dioxide (TiO2) particles can be used, for example, in roofing granules, to provide photocatalytic activity. To achieve long-term photocatalytic performance, a relatively high amount of silicate can be used in the coating composition. This may impact the color of the coated granules and reduce their photoactivity.